The present invention relates to the field of the landing of aircraft, in particular transport airplanes, on a landing area on the ground, in particular on a landing runway. A number of types of approaches can be used to land an aircraft, corresponding to a more or less automatic landing. Possible approaches are notably dependent on the equipment available on board the aircraft as well as the equipment available on the ground. For example, a fully automatic landing, category 3B, presupposes an airport equipped with so-called category 3B ILS (Instrument Landing System) instruments and an aircraft comprising systems compatible with these ILS instruments. When an automatic landing is not possible, the pilot of the aircraft must fly a landing by manual piloting. For such a landing, the aircraft is generally guided automatically, along its flight plane, as far as a height called “decision height,” then, if the visibility is sufficient at this decision height, the pilot controls the aircraft manually until it lands. The present invention relates more particularly to the phase corresponding to the flight of the aircraft between its passage at this decision height and its landing.
During the automatic guiding of the aircraft before it reaches the decision height, the systems of the aircraft handle its guidance along a predetermined trajectory by using either an external relative positioning system (notably of ILS type) which directly provides a trajectory deviation, or absolute aircraft positioning information available on board said aircraft as well as the geographic coordinates of the landing runway. This absolute position of the aircraft can notably be supplied by an inertial unit or by a system of VOR (Very High Frequency Omnidirectional Range) type or of GNSS (Global Navigation Satellite System) type, in particular of GPS (Global Positioning System) or Galileo type. Such a GNSS system can be augmented or not with a local adjustment, for example by using a WAAS (Wide Area Augmentation System) or EGNOS (European Geostationary Navigation Overlay Service) network. Like any measurement system, these systems provide the position of the aircraft with a determined accuracy and there is therefore a position error corresponding to the difference between the real position of the aircraft and the value of the position information available on board said aircraft. Consequently, during a transition, at the decision height, from automatic guidance to manual guidance of the aircraft, there is a position error between the real position of the aircraft and its theoretical position on said predetermined trajectory. The result of this is the drawback that, in the manual piloting to the landing, the pilot must carry out maneuvers to compensate this position error in order correctly to land the aircraft. This increases the workload of the pilot.
Document U.S. Pat. No. 5,593,114 A describes a system for assisting in the piloting of an aircraft in which a pilot has means enabling him or her to display a cursor on a screen where a landing runway is also displayed. The cursor comprises a cruciform symbol corresponding to a desired point of contact of the aircraft with the ground, as well as a line corresponding to an aircraft taxiing trajectory on the ground. The pilot has an interface enabling him or her to adjust the position and the orientation of the cursor on the landing runway. The system also displays a symbol corresponding to the speed vector of the aircraft. To be able to land on the runway, the pilot must align the symbol representing the speed vector with the cruciform symbol of the cursor. This system therefore assists the pilot during the landing by showing him or her this cursor on which he or she must align the symbol representing the speed vector. However, the movements of the aircraft during landing have the effect of producing movements of the cursor relative to the landing runway on the screen. This occurs in particular when the pilot is maneuvering the aircraft so as to try to align the symbol representing the speed vector with the cruciform symbol of the cursor. Consequently, depending on the movements of the aircraft, the pilot is required, several times during the landing, to have to modify the adjustment of the position and of the orientation of the cursor by means of said interface. This constitutes an additional workload for the pilot who has to constantly monitor the position and the orientation of the cursor in relation to the landing runway and modify them if necessary. Furthermore, such an operating mode is not compatible with an automatic aircraft landing when the pilot has to modify the settings of the cursor several times during the landing.